Why are you taking a level 0 (full) backup 6 days a week, and a level 1 only one day a week? Most people do just the opposite.
Why are you not backing up your archivelogs?
Why are you deleting your archivelogs without backing them up?
In a script, your 'delete obsolete' is expecting, and taking input from stdin, so when it prompts for 'yes' or 'no', it gets 'delete archivelog', etc.

Hi,
i've mixed up the days. Sorry. Of Course we're doing the full backup on monday and the "Level 1" backups on other days.
We're also backing up our archivelogs, but this is done in another script which runs every two hours.

Hi,
i've mixed up the days. Sorry. Of Course we're doing the full backup on monday and the "Level 1" backups on other days.
We're also backing up our archivelogs, but this is done in another script which runs every two hours.

WHat else have you "mixed up"?
The script(s) as shown will not run. I've already pointed out that your DELETE OBSOLETE is going to prompt for input from stdin. And I will now demonstrate that your DELETE ARCHIVELOG ALL will also prompt for input -- AND delete an archive log that has not been backed up.

Next a series of test scripts. Since this is Windows the scripting is more convoluted than if it were *nix
A script to generate some db activity and switch logfiles, thus simulating normal business activity. A sql script and a cmd script to call it:

set ORACLE_BASE=E:\app\oracle
set ORACLE_HOME=E:\app\oracle\product\11.2.0\dbhome_1
set ORACLE_SID=edstest
set PATH=E:\app\oracle\product\11.2.0\dbhome_1\bin;E:\app\oracle\product\11.2.0\dbhome_1\bin;E:\app\oracle\product\12.1.0\dbhome_1\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\
for /f "tokens=2 delims==" %%I in ('wmic os get localdatetime /format:list') do set datetime=%%I
set cdate=%datetime:~0,8%
set ctime=%datetime:~8,6%
set logfile=switch_logfile_%cdate%_%ctime%.log
sqlplus / as sysdba @switch_logfile > %logfile%
rem pause

A script to report the archivelog files:rpt_archivelogs.sql

set echo on feedback on verify on trimsp on lines 256 pages 60
col name for a55
conn / as sysdba
archive log list
select name,
status,
sequence#,
first_change#
from v$archived_log
where name is not null
order by name;
exit

And cmd file to call itrpt_archivelogs.cmd

set ORACLE_BASE=E:\app\oracle
set ORACLE_HOME=E:\app\oracle\product\11.2.0\dbhome_1
set ORACLE_SID=edstest
set PATH=E:\app\oracle\product\11.2.0\dbhome_1\bin;E:\app\oracle\product\11.2.0\dbhome_1\bin;E:\app\oracle\product\12.1.0\dbhome_1\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\
for /f "tokens=2 delims==" %%I in ('wmic os get localdatetime /format:list') do set datetime=%%I
set cdate=%datetime:~0,8%
set ctime=%datetime:~8,6%
set logfile=rpt_archlogs_%cdate%_%ctime%.log
sqlplus / as sysdba @rpt_archivelogs > %logfile%
rem pause

Scripts to implement your backup jobs (I've added a LIST BACKUP as the last step of each)backup_db_0.rman

set ORACLE_BASE=E:\app\oracle
set ORACLE_HOME=E:\app\oracle\product\11.2.0\dbhome_1
set ORACLE_SID=edstest
set PATH=E:\app\oracle\product\11.2.0\dbhome_1\bin;E:\app\oracle\product\11.2.0\dbhome_1\bin;E:\app\oracle\product\12.1.0\dbhome_1\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\
for /f "tokens=2 delims==" %%I in ('wmic os get localdatetime /format:list') do set datetime=%%I
set cdate=%datetime:~0,8%
set ctime=%datetime:~8,6%
set logfile=backup_db_0_%cdate%_%ctime%.log
rman target / @backup_db_0.rman > %logfile%
rem pause

set ORACLE_BASE=E:\app\oracle
set ORACLE_HOME=E:\app\oracle\product\11.2.0\dbhome_1
set ORACLE_SID=edstest
set PATH=E:\app\oracle\product\11.2.0\dbhome_1\bin;E:\app\oracle\product\11.2.0\dbhome_1\bin;E:\app\oracle\product\12.1.0\dbhome_1\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\
for /f "tokens=2 delims==" %%I in ('wmic os get localdatetime /format:list') do set datetime=%%I
set cdate=%datetime:~0,8%
set ctime=%datetime:~8,6%
set logfile=backup_db_1_%cdate%_%ctime%.log
rman target / @backup_db_1.rman > %logfile%
rem pause

set ORACLE_BASE=E:\app\oracle
set ORACLE_HOME=E:\app\oracle\product\11.2.0\dbhome_1
set ORACLE_SID=edstest
set PATH=E:\app\oracle\product\11.2.0\dbhome_1\bin;E:\app\oracle\product\11.2.0\dbhome_1\bin;E:\app\oracle\product\12.1.0\dbhome_1\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\
for /f "tokens=2 delims==" %%I in ('wmic os get localdatetime /format:list') do set datetime=%%I
set cdate=%datetime:~0,8%
set ctime=%datetime:~8,6%
set logfile=backup_archlogs_%cdate%_%ctime%.log
rman target / @backup_archlogs.rman > %logfile%
rem pause

And the results . . .
The first step, the first level 0 backup ran as expected and listed the two backupsets created at that time. I show just the LIST BACKUP. As you can see, there are no archivelogs yet backed up.

Next, we run the backup of archivelogs. The RMAN activity shows it backing up archlog seq 63, and 64. Backing up archivlogs also performs a log switch, which is how we got seq. 64. In the LIST BACKUP, notice backupset 75, containing the backup of archivelog seq 63 and 64.

So at this point you have deleted log seq 65 with no backup.You are now unrecoverable past sequence 64.
========================================================
Now, back to your original question, "rman does not delete "obsolete" backups on monday after". Let's move on past another cycle of generating activity and archlogs and move to the next level 0 backup: